Method of forming a selectively converted inter-layer dielectric using a porogen material

ABSTRACT

An inter-layer dielectric structure and method of making such structure are disclosed. A composite dielectric layer, initially comprising a porous matrix and a porogen, is formed. Subsequent to other processing treatments, the porogen is decomposed and removed from at least a portion of the porous matrix, leaving voids defined by the porous matrix in areas previously occupied by the porogen. The resultant structure has a desirably low k value as a result of the porosity and materials comprising the porous matrix and porogen. The composite dielectric layer may be used in concert with other dielectric layers of varying porosity, dimensions, and material properties to provide varied mechanical and electrical performance profiles.

RELATED APPLICATIONS

This application is a continuation-in-part of the patent applicationentitled, “Selectively Converted Inter-Layer Dielectric,” Ser. No.10/302,073, which was filed on Nov. 21, 2002, now U.S. Pat. No.6,943,121.

BACKGROUND OF THE INVENTION

Low dielectric constant materials are used as interlayer dielectrics inmicroelectronic structures, such as semiconductor structures, to reducethe RC delay and improve device performance. As device sizes continue toshrink, the dielectric constant of the material between metal lines mustalso decrease to maintain the improvement. Certain low-k materials havebeen proposed, including various carbon-containing materials such asorganic polymers and carbon-doped oxides. Although such materials mayserve to lower the dielectric constant, they may offer inferiormechanical properties such as poor strength and low fracture toughness.The eventual limit for a dielectric constant is k=1, which is the valuefor a vacuum. Methods and structures have been proposed to incorporatevoid spaces or “air gaps” in attempts to obtain dielectric constantscloser to k=1. One major issue facing low-k void technology is how toremove sacrificial material to facilitate multi-layer structures.Another major issue facing low-k void technology is how to facilitatevoid creation while providing a structure which can withstandconventional processing treatments, such as chemical-mechanicalpolishing and thermal treatment, as well as post processing mechanicaland thermo-mechanical rigors.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and is notlimited in the figures of the accompanying drawings, in which likereferences indicate similar elements. Features shown in the drawings arenot intended to be drawn to scale, nor are they intended to be shown inprecise positional relationship.

FIGS. 1A–1E depict cross-sectional views of various aspects of oneembodiment of the present invention incorporating a dielectric layerwhich may be modified using thermal or chemical treatments.

FIGS. 2A–2E depict cross-sectional views of various aspects of anotherembodiment of the present invention incorporating an additionaldielectric layer between the dielectric layer and the substrate.

DETAILED DESCRIPTION

In the following detailed description of embodiments of the invention,reference is made to the accompanying drawings in which like referencesindicate similar elements. The illustrative embodiments described hereinare disclosed in sufficient detail to enable those skilled in the art topractice the invention. The following detailed description is thereforenot to be taken in a limiting sense, and the scope of the invention isdefined only by the appended claims.

Referring to FIG. 1A, a substrate layer (100) is shown in cross sectionadjacent a first inter-layer dielectric (hereinafter “ILD”) layer (102).The substrate (100) may be any surface generated when making anintegrated circuit, upon which a conductive layer may be formed.Substrate (100) thus may comprise, for example, active and passivedevices that are formed on a silicon wafer, such as transistors,capacitors, resistors, diffused junctions, gate electrodes, localinterconnects, etcetera. Substrate (100) may also comprise insulatingmaterials (e.g., silicon dioxide, either undoped or doped withphosphorus or boron and phosphorus; silicon nitride; silicon oxynitride;or a polymer) that separate active and passive devices from theconductive layer or layers that are formed adjacent them, and maycomprise other previously formed conductive layers.

The first ILD layer (102) is a composite dielectric material comprisinga porous matrix material and a porogen material deposited together in asingle layer as shown, with the porogen occupying pores defined by theporous matrix. A distinction is made between a “porous” material havingpores, and a material having “voids”, voids differing from pores in thatvoids are substantially unoccupied by solid material, whereas pores mayor may not be so occupied. The porogen and matrix materials are selectedto enable selective decomposition and removal of the porogen, withoutsignificant detriment to the matrix material. Such a combination ofproperties allows for a controlled conversion between a first ILD layerwhich is substantially solid, mechanically relatively robust, andelectrically relatively high in capacitance, to a first ILD layer whichmay be substantially porous, mechanically weaker, and lower incapacitance at a desired point during the structure formation process.In particular, such a controlled conversion may be executed subsequentto process treatments where more mechanical robustness is preferred,such as polishing, trenching, and dielectric layer formation, as isdiscussed in further detail below.

The first ILD layer (102) may comprise a matrix material (“matrix”)having pores of relatively uniform size and distribution within thevolume occupied by the first ILD layer, the pores being substantiallyinterconnected to facilitate decomposition and removal of portions ofporogen material residing within the pores defined by the porous matrixmaterial, to convert the pertinent pores to voids. In one embodimentporous matrix may comprise an oxide material such as silicon dioxide ora compound having the molecular structure Si_(x) O_(y) R_(z), in which Rmay be selected from a group comprising hydrogen, carbon, an aliphatichydrocarbon and an aromatic hydrocarbon. When “R” is an alkyl or arylgroup, the resulting composition is often referred to as “carbon-dopedoxide” (“CDO”). When the porous matrix comprises a carbon-doped oxide,it may comprise between about 5 and about 50 atom % carbon. In anembodiment, such a compound includes about 15 atom % carbon. A polymericmaterial comprising crosslinked poly(phenylene), poly(arylether),polystyrene, crosslinked polyarylene, polymethylmethacrylate, aromaticpolycarbonate, aromatic polyimide, or silsesquioxanes such as methylsilsesquioxane (“MSQ”) and/or hydrogen silsesquioxane (“HSQ”) also maybe formed into porous matrix. While single-phase polymers by themselvesmay not form interconnected pores, several techniques are available tocause the polymers to form interconnected pores. In one embodiment,porogen particles having one dimension larger than the desired matrixfilm thickness may be used to ensure transport channeling across apolymer matrix. In another embodiment, modifications to the surfacechemistry of a porogen material, or the inherent surface chemistry ofporogen materials such as fumed silica, may produce an aggregatedstructure with high interconnectivity of porogens. In anotherembodiment, a polymer matrix may be combined with a sufficient amount ofporogen such that the porogen will define pore interconnectivity withina polymer matrix. It is known, for example, that porogen loading greaterthan about 30% by weight percentage is likely to result in poreinterconnectivity.

The completed microelectronic structure may have a first ILD layer (102)comprising a porous matrix with relatively high porosity. Using porousmatrix materials such as those mentioned herein, combined withstructure-enhancing removable porogens such as those discussed below,ILD structures having aggregate void volumes, defined as the sum of thevolumes of all pores not occupied by solid material, may be successfullyformed and left intact for subsequent device operation. In an embodimentthe aggregate void volume may be greater than 80% of the total volume ofthe ILD structure. Pores defined by the matrix may have sizes varyingfrom about 5 angstroms to about 100 nanometers in average diameter,depending upon the size of the porogen. The term “average diameter” maybe conventionally calculated as twice the cube root of (0.75*actual porevolume/pi), in reference to the fact that the pores generally are notperfectly spherical in shape. To facilitate the formation of otheradjacent layers with substantially uniform surfaces, pores larger than10 nanometers in diameter may not be desired in some embodiments.

In one embodiment, the porogen may be selectively decomposed and removedfrom the porous matrix of the first ILD layer on the basis ofdifferences in thermal decomposition temperatures between the porousmatrix material and the porogen. For example, a pairing of a porogenchosen from the group consisting of branched poly(p-xylene), linearpoly(p-phenylene), linear polybutadiene, and branched polyethylene,which have thermal decomposition temperatures of about 425–435 degreesC., about 420–430 degrees C., about 400–410 degrees C. and about 400–410degrees C., respectively, and a porous matrix material having a higherthermal decomposition temperature, suitable candidates comprisingcross-linked poly(phenylene), poly(arylether), aromatic polyimides, andaromatic polycarbonates, each of which has a thermal decompositiontemperature above 440 degrees C., may contribute to selective removal ofa thermally decomposed porogen, or a “porogen decomposition”, asfacilitated, for example, by introduction of an oxygen or hydrogen richcarrier plasma to carry away, or remove, the decomposition. Othersuitable materials for use as porogens, along with their respectivethermal decomposition temperatures, include but are not limited to:poly(ethylene terephthalate) (“PET”)—about 300 degrees C., polyamide-6,6(“Nylon 6/6”)—about 302 degrees C., syndiotactic polystyrene(“PS-syn”)—about 320 degrees C., poly(e-caprolactone) orpolycaprolactone—about 325 degrees C., poly(propylene oxide)(“PPO”)—about 325–375 degrees C., polycarbonates—about 325–375 degreesC., poly(phenylene sulfide) (“PPS”)—about 332 degrees C., polyamideimide(“PAI”)—about 343 degrees C., polyphthalamide (“PPA”, “Amodel”)—about350 degrees C., polymethylstyrene (“PMS”)—about 350–375 degrees C.,polyethretherketone (“PEEK”)—about 399 degrees C., poly(ether sulfone)(“PES”)—about 400 degrees C., poly(etherketone) (“PEK”)—about 405degrees C., polyoxymethlene (“POM”)—about 280 degrees C., poly (butyleneterephthalate) (“PBT”)—about 260 degrees C., and polystyrene (“PS”),about 260 degrees C. The materials, such as the polymers listed above,chosen as a porogen may have sufficient thermal stability to survivedual damascene processing through chemical-mechanical polishing steps,and may decompose into small molecular weight volatile fragments thatcan diffuse out of a cured matrix. In an embodiment, the porogen hassufficient thermal stability to survive process steps such as thin filmdeposition occurring at up to 300 degrees C. and metal cure occurring atup to 275 degrees C. Thermally decomposing a porogen material may befacilitated using heating equipment, such as a furnace or oven.Depending upon the materials selected, plasma tools may be appropriateas well.

In other embodiments, the porogens may be selectively decomposed withoutsubstantial decomposition of the aforementioned porous matrix materialsby introducing chemical solvents and agents, such as propylene glycolmonomethyl ether acetate, a versatile solvent used in many applications,cyclohexanone, a ketone solvent, ketenes such as 1-ene-3-cyclohexanone,hydrogen peroxide, tert-butyl peroxide, and solutions containing thecerium(IV) ion, to a porogen susceptible to chemical break-down by thepertinent chemical agents, and to matrix which preferably is notsubstantially effected by such chemical agent exposure. Many of theaforementioned polymeric porogen materials may be used in suchembodiments. Polymeric porogen materials may be functionalized withpolar groups such as hydroxy or alkoxy groups for solvent compatibilitywith the selected solvent or agent. To clarify the simplifiedterminology used herein as associated with the thermal or chemicalbreak-down of sacrificial materials for subsequent removal, referencesto “decompositions” and “decomposing” comprise reference to “dissolving”and “dissolution” as well, or more simply, “break-down” by thermal orchemical means.

Given the variety of suitable materials, many pairings of porous matrixand porogen may be successfully paired and selectively decomposed,depending upon the mode of decomposition, surrounding materials, andenvironmental limitations. Thermal and chemical modalities forfacilitating selective decomposition and removal of porogen materialsmay be used in some embodiments, in part because precise thermal andchemical treatments are known in microelectronic device processing. In athermal transformation embodiment, both the porous matrix and porogencomprise polymeric dielectric materials, the porous matrix having ahigher thermal decomposition temperature, in addition to a high glasstransition temperature for thermo-mechanical stability. With such apairing, the first ILD layer may be heated to a temperature above thethermal decomposition temperature for the porogen but below the thermaldecomposition temperature for the porous matrix, to facilitate removalof the porogen decomposition before subsequent cooling. In a chemicaltransformation embodiment, chemically-enhanced decomposition of theselected porogen material may result in substantially no decompositon ofthe associated porous matrix material or other adjacent materials.

Pairings of matrix and porogen materials, for example, include but arenot limited to: an oligomeric porogen, such as a low molecular weightpolystyrene, grafted as a side chain onto a tetraethylorthosilicate(“TEOS”) porous matrix polymer; crosslinked polyarylene matrix combinedwith polystyrene porogen; silicon dioxide matrix with polyethylene oxideporogen; silicon dioxide matrix with polynorbornene-based porogen suchas that sold under the trade name “Unity™400” by Promerus LLC; and CDOmatrix with polyethylene or polyethylene oxide porogen. Each of thesematrix materials has a higher thermal decomposition temperature ascompared with the matched porogen, and is substantially insoluble inconventional chemical agents and solvents such as those mentioned above,while the paired porogens are soluble in such agents and solvents. Interms of thermal decomposition temperatures, low molecular weightpolystyrene, polystyrene, polyethylene oxide, and polynorbornenethermally decompose at about 375, 375, 350, and 400–425 degrees Celsius,respectively, while TEOS and silicon dioxide thermally decompose attemperatures over 500 degrees Celsius, and crosslinked polyarylenethermally decomposes at about 400 degrees Celsius. Therefore, selectivedecomposition, either chemical or thermal, may be utilized to separatethese pairings.

Referring back to FIG. 1A, the first ILD layer (102) may be formedadjacent the substrate layer (100) using a variety of techniques, suchas spin-on or spin coating, spin-casting out of solution, evaporativedeposition, chemical vapor deposition, or plasma-enhanced chemical vapordeposition, depending upon the particular materials selected as porogenand porous matrix. The first ILD layer (102) may have a thicknessbetween about 10 nanometers to about 2,000 nanometers. In the case ofspin coating or other deposition methods, solvent may be removed usingevaporative techniques.

Referring to FIG. 1B, two conductive layers (104, 107) are showncrossing the first ILD layer (102). Each of the conductive layers (104,107) may comprise materials used to form conductive layers in integratedcircuits, such as one or more of metals such as copper, aluminum, andalloys thereof. For example, the depicted embodiment may be formed usingdual damascene techniques, wherein a trench (114) may formed for eachconductive layer using lithography, etching, and cleaning techniques,the trench having a via portion (118) and a line portion (116), the lineportion (116) having a width that may be between about 10 nanometers andabout 2,000 nanometers. The trench may then be lined with a barrierlayer (not shown) to isolate conductive material, after which the trench(114) may be filled with a conductive material using, for example,electroplating, chemical vapor deposition, or physical depositiontechniques, to form a conductive layer such as those depicted (104,107). With copper metal conductive layers, a barrier layer comprising,for example, tantalum, tantalum nitride or tungsten, may be effectivefor isolating the copper. Such barrier layers may be deposited usingtechniques such as chemical vapor deposition, atomic layer deposition,or other techniques. Polymeric barrier layers may also be employed, andmay be selected from the subgroup of polymer barrier materials whichhave relatively good electromigration characteristics. Alternatively, aconductive layer (104) may be made from doped polysilicon or a silicide,e.g., a silicide comprising tungsten, titanium, nickel, or cobalt.

The resultant interconnect layer (105) has conductive layers (104, 107)positioned between remaining portions of the first ILD layer (102). Thespacing between the conductive layers (104, 107) may vary with thefeature size of the microelectronic structure and may be between about10 nanometers and about 1,000 nanometers.

It is important to note that while a damascene type process isillustrated in reference to FIGS. 1B–1C and 2B–2C, wherein theconductive layer is formed into trenches using electroplatingtechniques, the dielectric aspect of the invention, illustrated insummary fashion with the transformation from structures like that ofFIG. 2C to structures like that of FIG. 2D, may be similarly applied tostructures formed using other techniques for forming conductive layers,such as subtractive metallization, given that the appropriate materialsare in place as further described herein. As would be apparent to oneskilled in the art, subtractive metallization may involve formation ofadjacent dielectric layers after formation of conductive layers, and thegeometries of conductive layers formed may vary from those availablewith electroplating processes such as dual damascene.

Depending upon the selected conductive material, a shunt layer may beformed over the conductive layers using conventional techniques andmaterials, to isolate the conductive layers from subsequent treatmentsand materials. With copper metal conductive layers, a metal shunt layercomprising, for example, cobalt or tungsten, may be effective forisolating the copper. The shunt material may be deposited usingtechniques such as chemical vapor deposition, subsequent to aplanarization treatment using techniques such as chemical-mechanicalplanarization (hereinafter “CMP”). Shunt material deposited upon theexposed portions of the first ILD layer (102) may be removed usingsubsequent CMP or etch back. The depiction in FIG. 1C shows suchportions already removed, resulting in two smaller shunt layers (120,121) substantially covering the conductive layers (104, 107) at athickness that may be between about 5 nanometers and about 100nanometers. Shunt materials such as tungsten may also be selectivelydeposited using techniques such as electroless processing, whichgenerally obviate the need for etch back or CMP to remove shunt materialfrom adjacent dielectric layers.

Referring to FIG. 1D, the structure of FIG. 1C is shown subsequent to acontrolled decomposition and removal of at least a portion of theporogen material, leaving the first ILD layer (102) to comprise theremaining porous matrix material (106) and any residual porogen (notshown). As discussed above in reference to FIG. 1A, the transformationfrom the embodiment of FIG. 1C, which may be more mechanically robustand higher in capacitance, to the embodiment of FIG. 1D, which may beless mechanically robust and lower in capacitance, may be controlled bya porogen decomposition and removal subprocess which leaves the porousmatrix and other structures intact, and a diffusion pathway of voidsdefined by the porous matrix. The embodiment of FIG. 1C where theporogens substantially fill pores in the dielectric layer (102), whichmay be more mechanically robust, may allow the dielectric layer (102) tobetter withstand processing steps to form structures such as theconductive layers (104, 107) and other structures than the embodiment ofFIG. 1D where the porogen material has substantially been removed toleave voids in the dielectric layer (102).

Subsequent to the decomposition of at least a portion of the porogenusing thermal energy, selective chemical solvents or agents, or otherknown selective decomposition techniques, the porogen decomposition or aportion thereof is removed from the first ILD layer (102), leaving voidsdefined by the matrix and any remaining porogen. With the aforementionedselective decomposition modalities, the porogen may be decomposedwithout substantial decomposition of the matrix. Selective thermaldecomposition may comprise heating the porogen and matrix to atemperature above the thermal decomposition temperature of the porogenmaterial, and below the thermal decomposition temperature of the matrix.Selective chemical decomposition may comprise exposing the porogen andmatrix to a chemical agent which breaks up, dissolves, or decomposes theporogen, without any substantial effect to the matrix (“selective” tothe porogen). Removal of decompositions may occur as a byproduct ofdecomposition process, as in a scenario wherein gases carrying portionsof a porogen decomposition may be exhausted away from the porous matrixmaterial given an available gradient pathway, or may occur asfacilitated by introduction of reactive carriers within the proximity ofthe porogen decomposition. Reactive carriers that may be used, or“carrier plasmas”, may include oxygen and hydrogen rich plasmas, whichmay actively absorb and transport materials or portions thereof due totheir high reactivity. Chemical cleaning or etching agents, such assupercritical carbon dioxide, which may absorb and transport decomposedmaterials, may also be used to remove porogen decompositions. Forexample, a porogen decomposition may be removed with the introductionand removal of supercritical carbon dioxide to carry the porogendecomposition away from the matrix. Therefore the “removing” subprocessmay comprise an active or passive subprocess; active in the scenariowherein a gradient is actively created through, for example,introduction of a carrier plasma, and passive in the scenario wherein agradient is present and a decomposition is allowed, for example, toexhaust away.

Referring to FIG. 1E, a dielectric layer (122) is shown adjacent theshunts (120, 121) and exposed portions of the first ILD layer (102). Thedielectric layer (122) may comprise an etch stop material such assilicon nitride, to assist in the formation of subsequent layers as isknown in the art. It may also comprise a dielectric or other materialsubstantially impermeable to liquids and gases, to prevent interactionbetween subsequently formed layers and the transformed first ILD layer(102). The dielectric layer (122) may also comprise conventional spin-onglass or spin-on polymeric dielectric materials, orchemical-vapor-deposited films such as silicon carbide. It may bedesirable, for example, to position a dielectric layer (122) which notonly provides a relatively uniform surface onto which subsequent layersmay be successfully formed, but also seals in gases such as tracehydrocarbons which may reside within the voids of the transformed firstILD layer (102). Indeed, an optional process treatment (not shown) isthe introduction of gas, such as nitrogen or argon and/or other inertgases, into the voids of the first ILD layer (102), the gas beingselected to improve electrical, thermal, corrosion, and/or processingproperties of the associated structures. High thermal conductivitygases, such as hydrogen or helium, may also be introduced into thevoids. The dielectric layer (122) may be deposited with a thicknessbetween about 5 nanometers and about 100 nanometers in an embodiment. Inanother embodiment the dielectric layer (122) may be deposited with athickness between about 10 nanometers and about 50 nanometers.

Referring to FIGS. 2A–2E, another embodiment of the invention isdepicted, this embodiment varying from that of FIGS. 1A–1E in that asecond ILD layer (124) is positioned between the first ILD layer (102)and the substrate layer (100). Such an embodiment may be used to providea structure with hybrid mechanical and electrical qualities. Forinstance, the second ILD layer (124) may comprise a dielectric materialwhich is higher in mechanical strength and electrical capacitance thanthe first ILD layer (102)—particularly after a first ILD layer (102) hasbeen transformed by decomposition and removal of the porogen comprisingthe first ILD layer (102), resulting in a structure such as thatdepicted in FIG. 2D. Referring to FIG. 2B, the illustrative embodimentof the second ILD layer (124) is located adjacent the via portion (118)of the conductive layer, while the line portion (116) is adjacent thefirst ILD layer (102). Such a configuration adds sustained mechanicalintegrity to the relatively narrow via portion (118), and also providesdesirable insulative properties most closely adjacent the line portion(116) of the conductive layer. Referring back to FIG. 2A, the second ILDlayer (124) may comprise any material that may insulate one conductivelayer from another, and preferably comprises a material appropriatelymatched with materials comprising the first ILD layer in accordance withthe desired modality of decomposition to enable the second ILD layer toremain structurally intact. For example, if a porogen comprising thefirst ILD layer is to be thermally decomposed, the material comprisingthe second ILD layer preferably has a relatively higher thermaldecomposition temperature. Similarly, if a porogen is to be chemicallydecomposed using a solvent, for example, the material comprising thesecond ILD layer preferably will be substantially insoluble in thepreferred solvent.

The second ILD layer (124) may comprise silicon dioxide (either undopedor doped with phosphorus or boron and phosphorus); silicon nitride;silicon oxy-nitride; porous oxide; an organic containing silicon oxide;a polymer; or another material. Silicon dioxide, silicon nitride, andsilicon oxy-nitride may have relatively high mechanical strengthcharacteristics as compared with many suitable porous matrix materials.Polymers or carbon doped oxides may also be used, as further describedabove, with a low dielectric constant that may be less than about 3.5 inan embodiment. In another embodiment, the dielectric constant may bebetween about 1.5 and about 3.0. The second ILD layer (124) may alsocomprise an organic polymer selected from a group that includespolyimides, parylene, polyarylethers, organosilicates, polynaphthalenes,polyquinolines, and copolymers thereof. For example, commerciallyavailable polymers sold by Honeywell Corporation and Dow ChemicalCorporation under the trade names FLARE™ and SiLK™, respectively, may beused to form the second ILD layer (124). The second ILD layer (124) mayalternatively comprise a carbon doped oxide, as described above.

Examples of other types of materials that may be used to form the secondILD layer (124) include aerogel, xerogel, and spin-on-glass (“SOG”). Inaddition, the second ILD layer (124) may comprise either hydrogensilsesquioxane (“HSQ”), methyl silsesquioxane (“MSQ”), or othermaterials having the molecular structure specified above, which may becoated onto the surface of a semiconductor wafer using a conventionalspin coating process. Although spin coating may be a way to form thesecond ILD layer (124) for some materials, for others chemical vapordeposition, plasma enhanced chemical vapor deposition, a SolGel process,or foaming techniques may be used.

The second ILD layer (124) may also comprise a porous matrix, or aporous matrix and removable porogen combination, analogous to thosedescribed above in reference to the dielectric layers (102) of FIGS. 1and 2. Some suitable second ILD layer (124) materials, such as thoseknown as “zeolites”, have naturally occurring interconnected pores.While the term “zeolite” has been used in reference to manyhighly-ordered mesoporous materials, several zeolites are known asdielectric materials, such as mesoporous silica and aluminosilicatezeolite materials. In embodiments wherein a porogen material of a firstILD layer and a porogen material comprising the second ILD layer (124)are similarly decomposable and removable, such decomposition and removalof porogens may be accomplished during the same set of subprocesses. Forexample, wherein both porogens are decomposable in the same solvent,both porogens may be decomposed and removed together. Similarly, inembodiments wherein both porogens have a similar thermal decompositiontemperature, they may be decomposed and removed together. Wherein thesecond ILD layer (124) comprises a polymer, it may be formed by spincoating or chemical vapor depositing the polymer onto the surface ofsubstrate (200). Zeolite materials may be synthesized by an aerogel orxerogel process, spin-coated into place, or deposited using chemicalvapor deposition to form a voided structure upon deposition. In the caseof spin coating or other deposition methods, solvent may be removedusing evaporative techniques. The second ILD layer (124) may have athickness between about 10 nanometers and about 1000 nanometers.

Referring to FIGS. 2B and 2C, conductive layers (104, 107) and shuntlayers (120, 121) may be formed in a similar manner as discussed abovein reference to FIGS. 1B and 1C. FIG. 2D depicts the structure of FIG.2C subsequent to controlled transformation of the first ILD layer (102)by selective decomposition and removal of the porogen, leaving theporous matrix (106) and any residual porogen to comprise the first ILDlayer (102). The embodiment of FIG. 2C where the porogens substantiallyfill pores in the dielectric layer (102), which may be more mechanicallyrobust, may allow the dielectric layer (102) to better withstandprocessing steps to form structures such as the conductive layers (104,107) and other structures than the embodiment of FIG. 2D where theporogen material has substantially been removed to leave voids in thedielectric layer (102). Once again, throughout the decomposition andremoval process, described in further detail in reference to FIG. 1D,the surrounding structures, including the second ILD layer (124) of theembodiment depicted in FIG. 2D, may remain substantially intact. FIG. 2Eshows the addition of a dielectric layer (122) similar to that of FIG.1E. Other various arrangements of layers of materials, such as thesecond ILD layer (124), and layers of the dielectric (102) with porogensin a porous matrix may also be formed.

Thus, a novel inter-layer dielectric solution is disclosed. Although theinvention is described herein with reference to specific embodiments,many modifications therein will readily occur to those of ordinary skillin the art. Accordingly, all such variations and modifications areincluded within the intended scope of the invention as defined by thefollowing claims.

1. A method comprising: forming a dielectric layer comprising a matrixmaterial with a plurality of pores and porogen material within thepores; removing at least some of the porogen material from at least someof the plurality of pores; and wherein the porogen material comprises amaterial selected from a group consisting of polyphenylene sulfide andpolybutylene terephthalate.
 2. The method of claim 1 wherein removing atleast some of the porogen material comprises thermally decomposing atleast some of the porogen material.
 3. The method of claim 2 furthercomprising depositing a thin film at a deposition temperature.
 4. Themethod of claim 3 wherein the porogen material has a thermaldecomposition temperature higher than the deposition temperature.
 5. Themethod of claim 4 wherein the deposition temperature is about 300degrees Celsius or lower.
 6. The method of claim 2 wherein the porogenmaterial has a thermal decomposition temperature lower than a thermaldecomposition temperature of the matrix material.
 7. A methodcomprising: forming a dielectric layer comprising a matrix material witha plurality of pores and porogen material within the pores; forming atrench in the dielectric layer; filling the trench with a conductivematerial, the filling being performed at a filling temperature; removingat least some of the porogen material from at least some of theplurality of pores; and wherein the porogen material comprises amaterial selected from a group consisting of polyphenylene sulfide andpolybutylene terephthalate.
 8. The method of claim 7 wherein the porogenmaterial has a thermal decomposition temperature higher than the fillingtemperature and lower than a thermal decomposition temperature of thematrix material.
 9. The method of claim 8 wherein the matrix materialcomprises a material selected from a group consisting of cross-linkedpolyphenylene, polyaryl ether, polystyrene, crosslinked polyarylene,polymethylmethacrylate, aromatic polycarbonate, aromatic polyimide,methyl silsesquioxane, and hydrogen silsesquioxane.
 10. The method ofclaim 1 wherein the porogen material comprises polybutyleneterephthalate.
 11. The method of claim 1 wherein the porogen materialcomprises polyphenylene sulfide.
 12. The method of claim 7 wherein theporogen material comprises polybutylene terephthalate.
 13. The method ofclaim 7 wherein the porogen material comprises polyphenylene sulfide.